The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Motorized vehicles may include a powertrain that includes a powerplant, such as an internal combustion engine, a multispeed transmission, and a differential or final drive train. The powerplant produces drive torque that is transmitted through one of various gear ratios of the transmission to the final drive train to drive wheels of the vehicle.
As an alternative to the internal combustion engine, automotive manufacturers have developed hybrid electric vehicles (HEVs). The hybrid powertrains of the HEVs may include both an electric drive system and an internal combustion (IC) engine that produce drive torque. During operation, HEVs use one or both of the power sources to improve efficiency.
The HEVs may use either a parallel drivetrain configuration or a series drivetrain configuration. In the parallel HEV, the electric drive system works in parallel with the IC engine to combine the power and range advantages of the IC engine with the efficiency and the electrical regeneration capability of the electric drive system. In the series HEV, the IC engine drives a generator to produce electricity for the electric machine, which drives a transaxle. This allows the electric machine to assume some of the power responsibilities of the IC engine, thereby permitting the use of a smaller and more efficient engine.
In both configurations, the electric drive system stores energy in batteries and uses the stored energy to power the vehicle. The HEV may shut down the IC engine when the vehicle is stopped or idling. On takeoff, the electric drive system may propel the vehicle and eventually restart the IC engine. The electric drive system stores braking energy in the batteries during regenerative braking.
The hybrid powertrain may be regulated by an electronic control system that includes one or more control modules. The control system may include an active fuel management (AFM) system that deactivates cylinders of the IC engine under low and/or moderate load conditions. For example, where the IC engine is provided with eight cylinders, the IC engine can be operated using four cylinders to improve fuel economy by reducing pumping losses.
As used herein, an activated mode refers to AFM operation using all of the engine cylinders. A deactivated mode refers to AFM operation using less than all of the cylinders of the IC engine (i.e. one or more cylinders are not active). A deactivation transition mode refers to a transition from the activated mode to the deactivated mode. An activation transition mode refers to a transition from the deactivated mode to the activated mode.
Transitions between the activated and deactivated modes may cause momentary drive torque disturbances that may be perceived by the driver and degrade the driving experience. For example, excess drive torque during the transitions may cause engine surge and insufficient torque may cause engine sag, both of which degrade the driving experience.
Conventional spark retard techniques have been used to compensate for the excess drive torque during the transitions. Retarding the spark delays the time to peak cylinder pressure which reduces the drive torque output of the IC engine. Additionally, techniques using the electric drive system have been used to smooth the drive torque disturbances occurring during the transitions by selectively generating or absorbing drive torque.